All news outlets have a bias, and they are going to ponder to the people that they serve. Fox news will put a republican spin on everything and CNN and MSNBC will put a left spin on everything. I am fairly certain that both sides have lied on the air at some point in the past election and they probably will in the next one too because they care more about money than the truth.
The mainstream media promoted the conspiracy theory that Saddam Hussein had weapons of mass destruction, which led to countless dead troops, the destabilization of an entire continent, and the rise of ISIS. NBC edited an audio tape to create the narrative that police were "racist". They produced the "hands up don't shoot" narrative, which led to riots in many cities. The main stream media promoted the "college rape culture" narrative. The mainstream media is pretty much a tool for the Democratic Party to try to influence people to vote for them without looking over their actual merits. Don't forget they created the narrative that Trump is "the next Hitler". On the anniversary of pearl harbor yesterday, they also worked to create the narrative that Trump will "put Muslims in internment camps".